Main performance indicators of lithium-ion batteries
Aug,02,24
The capacity of the battery
The capacity of a battery can be divided into rated capacity and actual capacity.
The rated capacity of a battery refers to the amount of electricity it should provide
when discharged at a rate of 5 hours to the termination voltage at an ambient temperature of 20 ℃± 5 ℃, denoted as C5.
The actual capacity of a battery refers to the actual amount of electricity released by the battery under certain discharge conditions,
mainly influenced by the discharge rate and temperature (therefore strictly speaking, the battery capacity should indicate the charging and discharging conditions).
Capacity unit: mAh, Ah (1Ah=1000mAh).
Internal resistance of battery
The internal resistance of a battery refers to the resistance experienced by the current flowing through its interior during operation.
It consists of two parts: ohmic resistance and polarization resistance.
A high internal resistance value of the battery can lead to a decrease in the discharge operating voltage and a shortened discharge time.
The magnitude of internal resistance is mainly influenced by factors such as battery material, manufacturing process, and battery structure.
The internal resistance of a battery is an important parameter for measuring its performance.
Voltage
Open circuit voltage refers to the potential difference between the positive and negative electrodes of a battery
when there is no current flowing through the circuit when the battery is not in operation.
In general, the open circuit voltage of a lithium-ion battery is around 4.1-4.2V when fully charged, and around 3.0V when discharged.
By detecting the open circuit voltage of the battery, the state of charge of the battery can be determined.
Working voltage, also known as terminal voltage, refers to the potential difference between the positive
and negative electrodes of a battery when there is current flowing through the circuit during operation.
In the discharge working state of the battery, when current flows through the inside of the battery,
there is no need to overcome the resistance caused by the internal resistance of the battery, so the working voltage is always lower than the open circuit voltage,
and the opposite is true during charging. The discharge operating voltage of lithium-ion batteries is around 3.6V.
Discharge platform time
The discharge platform time refers to the time it takes for a battery to discharge to a certain voltage when it is fully charged.
For example, measure the discharge plateau time of a certain ternary battery at 3.6V.
When the constant voltage is charged to a voltage of 4.2V and the charging current is less than 0.02C, stop charging to fully charge it, and then let it sit for 10 minutes.
The discharge plateau time at any rate of discharge current is the discharge plateau time at that current.
Due to the voltage requirements of some electrical appliances that use lithium-ion batteries, if the voltage is lower than the required value, it may result in malfunction.
So the discharge platform is one of the important criteria for measuring the performance of a battery.
Charge discharge rate
Charge discharge rate refers to the current value required for a battery to discharge its rated capacity within a specified time.
1C is numerically equal to the rated capacity of the battery and is usually represented by the letter C.
If the nominal rated capacity of the battery is 10Ah, then 10A is 1C (1 rate), 5A is 0.5C, 100A is 10C, and so on.
Self discharge rate
Self discharge rate, also known as charge retention capacity, refers to the ability of a battery to maintain the amount of stored electricity under certain conditions when in an open circuit state.
Mainly influenced by factors such as battery manufacturing process, materials, storage conditions, etc. It is an important parameter for measuring battery performance.
efficiency
Charging efficiency refers to the degree to which the electrical energy consumed by a battery during the charging process is converted into the chemical energy that the battery can store.
Mainly affected by battery technology, formula, and the working environment temperature of the battery, the higher the ambient temperature, the lower the charging efficiency.
Discharge efficiency refers to the ratio of the actual amount of electricity discharged to the terminal voltage under certain discharge conditions to the rated capacity of the battery.
It is mainly affected by factors such as discharge rate, ambient temperature, and internal resistance. Generally, the higher the discharge rate, the lower the discharge efficiency.
The lower the temperature, the lower the discharge efficiency.
cycle life
Battery cycle life refers to the number of charge and discharge cycles that a battery undergoes under a certain charging and discharging regime when its capacity drops to a specified value.
According to GB regulations, the capacity retention rate of lithium-ion batteries should be above 60% after 500 cycles under 1C conditions.
